Method for fabricating a liquid crystal display device and an LCD device thereby

ABSTRACT

A method for fabricating a LCD having enhanced aperture ratio and brightness includes: forming a gate line, a gate electrode, a common electrode and a common line in a first mask process; depositing a gate insulating layer covering the gate line, the gate electrode and the common electrode; forming an active layer on the gate insulating layer, and an ohmic contact layer on the active layer in a second mask process; forming a data line, a source electrode, and a drain electrode facing the source electrode in a third mask process; depositing a protective layer over the data line, the source electrode and the drain electrode; forming a pixel contact hole in a fourth mask process; and forming a pixel electrode, wherein the pixel electrode is connected to the drain electrode through the pixel contact hole in a fifth mask process using a reverse tapered photo-resist pattern.

This application claims the benefit of Korean Application No.10-2006-056848 filed on Jun. 23, 2006, which is hereby incorporated byreference all purposes as if fully set forth.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display device and amethod for fabricating the same. More particularly, the presentinvention relates to a method for fabricating a liquid crystal display(“LCD”) in which an aperture ratio and brightness are enhanced.

2. Discussion of the Related Art

The liquid crystal display (LCD) device displays includes a color filterarray panel and a thin film transistor (“TFT”) array panel facing eachother with a liquid crystal layer between them. The color filter arraypanel includes a black matrix for blocking the light leakage, a colorfilter of red, blue and green, and a leveling layer for leveling thesurface of the upper substrate. As illustrated in FIG. 1, the TFT arraysubstrate includes a gate line 2 and a data line 4 crossing each otheron a lower substrate, a TFT 30 at the crossing portion of the gate anddata lines, and a pixel electrode 18 formed in the pixel regionsurrounded by the gate line 2 and the data line 4.

The TFT 30 acts as a switch to supply an electric signal to the pixelelectrode 18. In the pixel area, a common electrode 22 generates ahorizontal electric field with the pixel electrode 18 to drive theliquid crystal layer, and a common line 20 connects a plurality ofcommon electrode 22.

In addition, the TFT array panel includes a gate pad (not shown) at theend of the gate line 2 and a data pad (not shown) at the end of the dataline 4. A scan signal is supplied to the gate line 2 from a gate driveIC (not shown) connected to the gate pad. A video data signal issupplied to the data line 4 from a data drive IC (not shown) connectedto the data pad.

The TFT 30 charges the video data signal supplied through the data line4 to the pixel electrode 18 by responding to the scan signal suppliedthrough the gate line 2. Therefore, the TFT 30 includes a gate electrode8 connected to the gate line 2, a source electrode 10 connected to thedata line 4, and a drain electrode 12 facing the source electrode 10 andconnected to the pixel electrode 18 through the contact hole 32. Thecommon line 20 supplies the base electric voltage to the commonelectrode 22 for generating the horizontal electric filed with the videodata signal supplied to the pixel electrode 18 to drive the liquidcrystal layer.

The common electrode 20 disposed in the pixel area of the LCD device ismade of the same material as the gate line 2 and common line 20, theconductive metal material not transparent the light. Further, the pixelelectrode 18 may include an opaque conductive metal material forreducing the line resistance. By the pixel electrode 18 and the commonelectrode 20 having an opaque material, the aperture ratio of the pixelregion will be degraded. As a result, the brightness of the LCD deviceis degraded also.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a method forfabricating a LCD device and the LCD in which the aperture ration of thepixel region is increased and the brightness of the LCD is enhanced bymaking the pixel electrode and the common electrode have the thinnestwidth while maintaining an optimized electric property.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. These andother advantages of the invention will be realized and attained by thestructure particularly pointed out in the written description and claimshereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, a method for fabricating a liquid crystaldisplay device, comprises: forming a gate line, a gate electrodeconnected to the gate line, a common electrode and a common lineconnected to the common electrode on a substrate in a first maskprocess; depositing a gate insulating layer on the substrate to coverthe gate line, the gate electrode and the common electrode; forming anactive layer on the gate insulating layer, the active layer overlappingthe gate electrode to form a channel layer, and forming an ohmic contactlayer on the active layer in a second mask process; forming a data linecrossing the gate line to define a pixel region, a source electrodeconnected to the data line, and a drain electrode facing with the sourceelectrode in a third mask process; depositing a protective layer overthe data line, the source electrode and the drain electrode; forming apixel contact hole that exposes the drain electrode by penetrating theprotective layer in a fourth mask process; and forming a pixel electrodethat generates a horizontal electric field with the common electrode inthe pixel region, wherein the pixel electrode is connected to the drainelectrode through the pixel contact hole in a fifth mask process using areverse tapered photo-resist pattern.

In another embodiment of the present invention, a method for fabricatinga liquid crystal display device, comprises: forming a gate line, a gateelectrode connected to the gate line, a common electrode and a commonline connected the common electrode on a substrate in a first maskprocess; depositing a gate insulating layer on the substrate to coverthe gate line, the gate electrode and the common electrode; forming anactive layer on the gate insulating layer, the active layer overlappingthe gate electrode to form a channel layer, and forming an ohmic contactlayer on the active layer, a data line crossing with the gate line todefine a pixel region and a source-drain pattern connecting to the dataline in a second mask process; depositing a protective layer over thedata line, the source electrode and the drain electrode; patterning thesource-drain pattern to form a source electrode and a drain electrode,completing the channel layer by removing a portion of the ohmic contactlayer between the source electrode and the drain electrode, and forminga pixel contact hole exposing the drain electrode by penetrating theprotective layer in a third mask process; and forming a pixel electrodethat generates a horizontal electric field with the common electrode inthe pixel region, wherein the pixel electrode connects to the drainelectrode through the pixel contact hole in a fourth mask process usinga reverse tapered photo-resist pattern.

In still another embodiment of the present invention, a method forfabricating a liquid crystal display device, comprises: forming a gateline and a gate electrode connected to the gate line on a lowersubstrate using a reverse tapered photo-resist pattern; forming a dataline crossing the gate line to define a pixel region, a source electrodeconnected to the data line, and a drain electrode facing the sourceelectrode on the lower substrate using a reverse tapered photo-resistpattern; forming a pixel electrode in the pixel region connecting to thedrain electrode on the lower substrate; and forming a common electrodeon a upper substrate facing the lower substrate to form a verticalelectric field with the pixel electrode.

In another embodiment, a liquid crystal display device comprises a gateline and a data line crossing each other to define a pixel region on alower substrate; a TFT disposed at the crossing portion of the gate lineand the data line; a pixel electrode connected to the TFT in the pixelregion; a common electrode in the pixel region facing the pixelelectrode to generate an in-plane electric field; and a common lineconnected to the common electrode to supply a base electric voltage tothe common electrode.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

In the drawings:

FIG. 1 illustrates a plan view of the TFT array panel according to therelated art;

FIG. 2 illustrates a plan view of a TFT array panel according to thefirst embodiment of the present invention;

FIG. 3 illustrates a cross sectional view along the cutting line I-I′ ofthe TFT array panel according to the first embodiment;

FIG. 4A illustrates a cross sectional view explaining the formation ofan electrode using a related art tapered photo-resist pattern;

FIG. 4B illustrates a cross sectional view explaining formation of theelectrode using a reverse tapered photo-resist pattern;

FIGS. 5A and 5B illustrate a plan view and a cross sectional viewdescribing the first mask process of a method for fabricating a TFTarray panel according to the first embodiment of the present invention;

FIGS. 6A and 6B illustrate a plan view and a cross sectional viewdescribing the second mask process of a method for fabricating a TFTarray panel according to the first embodiment of the present invention;

FIGS. 7A and 7B illustrate a plan view and a cross sectional viewdescribing the third mask process of a method for fabricating a TFTarray panel according to the first embodiment of the present invention;

FIGS. 8A and 8B illustrate a plan view and a cross sectional viewdescribing the fourth mask process of a method for fabricating a TFTarray panel according to the first embodiment of the present invention;

FIGS. 9A and 9B illustrate a plan view and a cross sectional viewdescribing the fifth mask process of a method for fabricating a TFTarray panel according to the first embodiment of the present invention

FIGS. 10A and 10B illustrate the brightness of the LCD according to therelated art and the brightness of the LCD according to the presentinvention, respectively;

FIG. 11 illustrate a plan view of a TFT array panel according to thesecond embodiment of the present invention;

FIG. 12 illustrates a cross sectional view along the cutting line II-II′of the TFT array panel of FIG. 11 according to the second embodiment.

FIGS. 13A and 13B illustrate a plan view and a cross sectional viewdescribing the first mask process of a method for fabricating a TFTarray panel according to the second embodiment of the present invention;

FIGS. 14A and 14B illustrate a plan view and a cross sectional viewdescribing the second mask process of a method for fabricating a TFTarray panel according to the second embodiment of the present invention;

FIGS. 15A and 15B illustrate a plan view and a cross sectional viewdescribing the third mask process of a method for fabricating a TFTarray panel according to the second embodiment of the present invention;and

FIGS. 16A and 16B illustrate a plan view and a cross sectional viewdescribing the fourth mask process of a method for fabricating a TFTarray panel according to the second embodiment of the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Reference will now be made in detail to embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings.

FIG. 2 is a plan view illustrating the TFT array panel according to thepresent invention. FIG. 3 is a cross sectional view of the TFT arraypanel shown in FIG. 2 along the cutting line I-I′.

Referring to the FIGS. 2 and 3, the TFT array panel according to thepresent invention includes a gate line 102 and a data line 104 crossingeach other with a gate insulating layer 124 between them to define apixel region on a lower substrate 100; a pixel electrode 118 and acommon electrode 122 generating a horizontal electric field in the pixelarea; a TFT 130 connected to the gate line 102, the data line 104 andthe pixel electrode 118; and a common line 120 connected to the commonelectrode 122. Further, the TFT array panel includes a storage capacitor140 formed at the overlap area between common line 120 and the drainelectrode 122 with the gate insulating layer 124 between them, a gatepad (not shown) at the end of the gate line 102, and a data pad (notshown) at the end of the data line 104.

The scan signal is supplied to the gate line 102 from the gate drive IC(not shown) connected to the gate pad. The video data signal is suppliedto the data line 104 from the data drive IC (not shown) connected to thedata pad. The TFT 130 charges the video data signal supplied from thedata line 104 to the pixel electrode 118 responding to the scan signalsupplied from the gate line 102. The TFT 130 functions as a switch tosupply the video data signal to the pixel electrode from the data lineand includes a gate electrode 108 connected to the gate line 102, asource electrode 110 connected to the data line 104, a drain electrode112 facing the source electrode 110 and connected to the pixel electrode118 through the pixel contact hole 132, an active layer 126 overlappingthe gate electrode 108 with the gate insulating layer 124 and forming achannel between the source electrode 110 and the drain electrode 112,and a ohmic contact layer 128 reducing the contact resistance betweenthe active layer 126 and the source electrode 110 or the drain electrode112.

The common line 120 supplies the base voltage to the common electrode122 for generating the horizontal electric field by corresponding to thevideo data signal supplied to the pixel electrode 118. The pixelelectrode 118 and the common electrode 122 are disposed substantially inparallel to each other within the pixel region which is surrounded bythe gate line 102 and the data line 104 crossing each other.

The pixel electrode 118 is made of, for example, a transparentconductive material including ITO (Indium Tin Oxide), IZO (Indium ZincOxide) or ITZO (Indium Tin Zinc Oxide). To reduce the electricresistance of the pixel electrode 118, the pixel electrode 118 mayfurther include a non-transparent conductive material such as molybdenum(Mo), Titanium (Ti), Copper (Cu), Aluminum Neodium (AlNd), Chromium(Cr), Molybdenum alloy, Copper alloy or Aluminum alloy. The commonelectrode 122 is generally made of, for examples, a non-transparentconductive material including molybdenum (Mo), Titanium (Ti), Copper(Cu), Aluminum Neodium (AlNd), Chromium (Cr), Molybdenum alloy, Copperalloy or Aluminum alloy.

The pixel electrode 118 and the common electrode 122, as shown in FIG.2, may be formed in a linear line shape, a zigzag shape or other shapeswith the data line 104. Further, the pixel electrode 118 and the commonelectrode 122 may be formed in the zigzag shape, while the data line 104is formed in the linear line shape. The conductive line patterns of theTFT array panel according to the present invention such as the pixelelectrode 118, the common electrode 122, the gate line 102 and the dataline 104 are formed with the reverse tapered photo-resist pattern.

The tapered photo-resist pattern generally used in the related artmanufacturing method typically has the bottom width wider than the upperwidth, as shown in FIG. 4A. For example, the conductive metal line maybe formed by a wet etching method in which the line width of thephoto-resist is 4.5 μm and the CD (Critical Dimension) loss, permissibletolerance of etching process, is 1 μm. In that case, the line width ofthe tapered photo-resist pattern 201 has the bottom width of 4.5 μm.Patterning the conductive metal line 211 with this photo-resist pattern,by the CD loss due to under-cut phenomena, the patterned line width ofthe conductive metal line 211 will be 3.5 μm. The CD loss is the processtolerance occurred in the etching process which is hard to control.Therefore, it is hard to control the line width by adjusting the CDloss. That is, for patterning the conductive metal line narrower than3.5 μm, the width of the photo-resist should be formed less than 4.5 μm.

The reverse tapered photo-resist pattern used in the present inventionhas the bottom width more narrow than the upper width, as shown in FIG.4B. Therefore, even when the line width of the photo-resist pattern 301is formed to be about 4.5 μm, the bottom width of the photo-resistpattern 301 is narrower than 4.5 μm because of the reverse tapering. Asthe focus is increased and the exposure is increased, the bottom widthof the reverse tapered photo-resist pattern is narrowed. Actually,adjusting the defocus and exposure amounts in the exposing process forpatterning the photo-resist, the bottom of the reverse taperedphoto-resist pattern is formed to have any one width value from about2.5 μm to about 4.5 μm. Further, the bottom width of the reverse taperedphoto-resist pattern can be formed more narrowly by controlling thetemperature of the baking process after coating the photo-resist.Consequently, controlling the temperature in the backing process afterdepositing the photo-resist and adjusting the defocus and exposureamount in the exposing process, the bottom width of the reverse taperedphoto-resist pattern can be one of about 2˜4.5 μm. Etching theconductive metal layer 311 with the reverse tapered photo-resist pattern301 having about 2˜4.5 μm bottom width, considering the CD loss, themetal layer 311 can be patterned to have about 1.5˜4.0 μm width. Thus,by adjusting the processing condition, CD loss can be controlled withinabout 1 μm to about 0.5 μm. As a result, using the reverse taperedphoto-resist pattern, the metal pattern can be formed to have any onewidth from a very fine width (about 1.5 μm) to a photo-resist width ofabout 4.0 μm just by variously controlling the processing condition withthe same photo-resist width precision.

In a method for fabricating the TFT array panel according to the presentinvention, the conductive patterns including the pixel electrode 118,the common electrode 122, the gate line 102 and the data line 104 can beformed to have any one width of about 1.5˜4.0 μm by patterning in theetching process using the reverse tapered photo-resist pattern havingabout 4.5 μm line width.

Reducing the line widths of the pixel electrode 118 and the commonelectrode 122 formed in the pixel region by the same patterningdimension with the related art method, the aperture ratio of the pixelregion can be increased. As a result, the brightness of the TFT arraypanel according to the present invention can be enhanced.

Additionally, as the line width of the conductive pattern is remarkablyreduced, the pixel number can be increased proportional to the areacorresponding to the reduced line width under the same aperture ratiocondition. That is, with the same aperture ratio, the pixel number isincreased and the TFT panel according to the present invention suggestsa higher resolution panel.

Referring to FIGS. 5A to 9B, a method for fabricating the TFT arraypanel including 5 mask processes according to the first embodiment ofthe present invention will be explained. FIGS. 5A and 5B illustrate thefirst mask process of the method for fabricating the TFT array panel. Onthe lower substrate 100, a gate line 102, a gate pad (not shown), a gateelectrode (108), a common line 120 and a common electrode 122 areformed.

In detail, using a deposition process such as sputtering, a gate metalmaterial is deposited on the whole surface of the lower substrate 100.Subsequently, in a photo-lithography process using a first mask, areverse tapered photo-resist pattern is formed on the gate metalmaterial, and then, in an etching process, the gate metal material ispatterned with the reverse tapered photo-resist pattern as a mask. Then,the gate line 102, the gate pad at the end of the gate line 102, thegate electrode 108 connecting to the gate line 102, the common line 120and the common electrode 122 connected to the common line 120 areformed. The gate metal material includes at least one of, for example,molybdenum (Mo), Titanium (Ti), Copper (Cu), Aluminum Neodium (AlNd),Chromium (Cr), Molybdenum alloy, Copper alloy or Aluminum alloy. Asthese conductive materials are non-transparent materials, in order toenhance the aperture ratio, these patterns are preferably formed usingthe reverse tapered photo-resist pattern as a mask to have finer linewidths.

Referring to the FIGS. 6A and 6B, in the second mask process, an activelayer 126 and an ohmic contact layer 128 are formed on the lowersubstrate 100 having the gate line 102, the gate pad, the gate electrode108, the common line 120 and the common electrode 122. Using adepositing process such as a PECVD method, a gate insulating layer 124,an amorphous silicon layer and an impurity (n+ or p+) doped amorphoussilicon layer are deposited on the lower substrate 100. Subsequently, ina photo-lithography process using the second mask, a reverse taperedphoto-resist pattern is formed, and then in the etching process, theimpurity doped amorphous silicon layer and the amorphous silicon layerare patterned using the reverse tapered photo-resist pattern as a mask.Then, the active layer 126 forms a channel of the TFT on the gateinsulating 124 overlapping with the gate electrode 108 and the ohmiccontact layer 128 overlapping with the active layer 126. The gateinsulating layer includes the inorganic insulating material such assilicon oxide (SiOx) or silicon nitride (SiNx).

Referring to the FIGS. 7A and 7B illustrating the third mask process, adata line 104, a data pad (not shown), a source electrode 110 and adrain electrode 112 are formed on the lower substrate 100 having theactive layer 126 and the ohmic contact layer 128. Using a depositingprocess such as a sputtering method, a source/drain metal layer isdeposited on the whole surface of the lower substrate 100. Subsequently,in a photo-lithography process using the third mask, the reverse taperedphoto-resist pattern is formed, and then in the etching process, thesource/drain metal layer is patterned using the reverse taperedphoto-resist pattern as a mask. Then, the data line 104 crossing withthe gate line 102, the data pad at the end of the data line 104, thesource electrode 110 connected to the data line 104 and the drainelectrode 112 facing the source electrode 110. Here, some portions ofohmic contact layer 128 between the source electrode 110 and the drainelectrode 112 are removed to complete the channel of the TFT. Thesource/drain metal includes at least one of molybdenum (Mo), Titanium(Ti), Copper (Cu), Aluminum Neodium (AlNd), Chromium (Cr), Molybdenumalloy, Copper alloy or Aluminum alloy. As these conductive materials arenon-transparent materials, in order to enhance the aperture ratio, thesepatterns are preferably formed using the reverse tapered photo-resistpattern as a mask to have finer line widths.

Referring to the FIGS. 8A and 8B illustrating the fourth mask process, aprotective layer 130 is formed to cover the entire surface (except thepixel contact hole 132) of the lower substrate 100 having the data line104, the data pad, the source electrode 110 and the drain electrode 112.In detail, the protective layer 130 is deposited on the whole surface ofthe lower substrate 100 using a deposition process such as the PECVDmethod. Subsequently, in the photo-lithography process using the fourthmask and the etching process, the pixel contact hole 132 exposes someportions of the drain electrode 112 by penetrating the protective layer130. Here, a gate pad contact hole (not shown) exposes the gate pad atthe end of the gate line 102 by penetrating the gate insulating layer124 and the protective layer 130, and a data pad contact hole (notshown) exposes the data pad (not shown) at the end of the data line 104by penetrating the protective layer 130 may be formed with the pixelcontact hole 132.

Referring to FIGS. 9A and 9B, in the fifth mask process, a pixelelectrode 118 is formed on the lower substrate 100 having the protectivelayer 130. In detail, using a depositing process such as a sputteringmethod, a pixel material is deposited on the whole surface of the lowersubstrate 100. Subsequently, in the photo-lithography process using thefifth mask, the reverse tapered photo-resist pattern is formed, and thenin the etching process, the pixel material is patterned. Then, the pixelelectrode 118 is formed in the pixel region with contacting to the drainelectrode 112 through the pixel contact hole 132 and being substantiallyparallel with the common electrode 122. The pixel material includes atransparent conductive material such as ITO (Indium Tin Oxide), IZO(Indium Zinc Oxide) or ITZO (Indium Tin Zinc Oxide). Further, the pixelmaterial may include a non-transparent conductive material such asmolybdenum (Mo), Titanium (Ti), Copper (Cu), Aluminum Neodium (AlNd),Chromium (Cr), Molybdenum alloy, Copper alloy or Aluminum alloy. When anon-transparent conductive material is included in the pixel material,in order to enhance the aperture ratio, the patterns are preferablyformed using the reverse tapered photo-resist pattern as a mask to havefiner line widths.

Based upon the above described method for fabricating the TFT arraypanel, the conductive patterns such as the pixel electrode 118, thecommon electrode 122, the gate line 102 and the data line 104 can beformed with about 1.5˜4.0 μm line widths using the reverse taperedphoto-resist pattern having the 4.5 μm line width. Therefore, the linewidths of the pixel electrode 118 and the common electrode 122 formed inthe pixel region can be reduced and then the aperture ratio can beincreased. The brightness of the TFT array panel according to thepresent invention as shown in FIG. 10B is enhanced over than thebrightness of the TFT array panel according to the related art as shownin FIG. 10A.

In the first embodiment, all conductive patterns including pixelelectrode 118, common electrode 122, gate line 102 and data line 104 areformed using reverse tapered photo-resist patterns. Considering the mainpurpose of this invention is focused on to increase the aperture ratioof the pixel region, the reverse tapered photo-resist pattern is usedjust in the fifth mask process for making the pixel electrode 118.

FIG. 11 illustrates the plan view of the TFT array panel according tothe second embodiment of the present invention. FIG. 12 illustrates thecross sectional view along the cutting line II-II′ of FIG. 11 accordingto the second embodiment of the present invention. Referring to FIGS. 11and 12, the TFT array panel according to the second embodiment is thesame as that of the first embodiment except that the active layer 126and the ohmic contact layer 128 are formed to have substantially thesame size as the data line 104, the source electrode 110 and the drainelectrode 112. Referring to the FIGS. 13A to 16B, a method forfabricating the TFT array panel with fourth mask processes according tothe second embodiment of the present invention will be explained.

Referring to the FIGS. 13A and 13B, in the first mask process, a gateline 102, a gate pad (not shown), a gate electrode 108, a common line120 and a common electrode 122 are formed on a lower substrate 100.Using a deposit process such as a sputtering method, a gate metal layeris deposited on the whole surface of the lower substrate 100.Subsequently, in a photo-lithography process using the first mask, areverse tapered photo-resist pattern is formed on the gate metal layer,and then, in an etching process, the gate metal layer is patterned usingthe reverse tapered photo-resist pattern as a mask. Then, the gate line102, the gate pad at the end of the gate line 102, the gate electrode108 connected to the gate line 102, the common line 120 and the commonelectrode 122 connected to the common line 120 are formed.

Referring to the FIGS. 14A and 14B, in the second mask process, anactive layer 126, an ohmic contact layer 126, a data line 104, a datapad (not shown) and a source-drain pattern 110 a not separated butformed in one pattern on the lower substrate 110 having the gate line102, the gate pad, the gate electrode 108, the common line 120 and thecommon electrode 122. Using a depositing process such as a PECVD method,a gate insulating layer 124, an amorphous silicon layer and an impuritydoped (n+ or p+) amorphous silicon layer are deposited on the wholesurface of the lower substrate 100. Sequentially, using the sputteringmethod, a source/drain metal layer is deposited thereon. Subsequently,in the photo-lithography process using the second mask, a reversetapered photo-resist pattern is formed, and then in the etching process,the source/drain metal layer, the impurity doped amorphous silicon layerand the amorphous silicon layer are patterned by the reverse taperedphoto-resist pattern as a mask. Then, the data line 104 crossing thegate line and the data pad at the end of the data line 104 are formed.Further, the source-drain pattern 110 a which will be separated into thesource electrode connecting to the data line 104 and the drain electrodefacing with the source electrode is formed. Under the source-drainpattern 110 a, there are the active layer 126 forming the channelbetween the source electrode and drain electrode, and the ohmic contactlayer 128 for reducing the contact resistance between the active layer126 and the source-drain electrodes. At this time, the data line andsource-drain pattern 110 a, the active layer 126 and the ohmic contactlayer 128 have the same shape because they are patterned at the sametime with the same mask.

Referring to the FIGS. 15A and 15B, in the third mask process, aprotective layer 130 covers the whole surface of the lower substrate 100(except a pixel contact hole 132 and a channel of the TFT) including thedata line 104, data pad, source electrode 110 and drain electrode 112.The protective layer 130 is deposited on the whole surface of the lowersubstrate 100 using a PECVD method. Subsequently, a photo-lithographyprocess and etching process using the third mask process, the pixelcontact hole 132 exposing some portions of the drain electrode 112 bypenetrating the protective layer 130. Further, the source electrode 110and the drain electrode 112 are separated. And then, the exposed ohmiccontact layer 128 between the source electrode 110 and the drainelectrode 112 should be removed by oxidizing with oxygen plasma tocomplete the channel layer. Then, the TFT is completely formed. Here, agate pad contact hole (not shown) exposing the gate pad at the end ofthe gate line 102 by penetrating the gate insulating layer 124 and theprotective layer 130, and a data pad contact hole (not shown) exposingthe data pad (not shown) at the end of the data line 104 by penetratingthe protective layer 130 may be formed with the pixel contact hole 132.

Referring to FIGS. 16A and 16B, in the fourth mask process, a pixelelectrode 118 is formed on the lower substrate 100 having the protectivelayer 130. Using a depositing process such as sputtering method, a pixelmaterial is deposited on the whole surface of the lower substrate 100.Subsequently, in the photo-lithography process using the fourth mask, areverse tapered photo-resist pattern is formed, and then in the etchingprocess, the pixel material is patterned with the reverse taperedphoto-resist pattern as a mask. Then, the pixel electrode 118 is formedin the pixel region. The pixel electrode contacts the drain electrode112 through the pixel contact hole 132 and is substantially parallel tothe common electrode 122.

The method for fabricating the TFT array panel according to the secondembodiment of the present invention uses four mask processes so that themanufacturing price can be reduced. Further, the present invention doesnot use a half tone mask or refraction mask, which are relatively highin price, to reduce the mask process number for manufacturing the TFTarray panel so that it can more save the fabricating price.

In the first and the second embodiments, the present invention isapplied to an IPS mode LCD device in which the pixel electrode 118 andthe common electrode 122 are formed on the lower substrate 100. However,the features of the present invention can be applied to a verticalelectric field type LCD panel in which the pixel electrode is formed onthe lower substrate and the common electrode is formed on the uppersubstrate facing the lower substrate. When the conductive patterns areformed in the vertical electric field type LCD by using the reversetapered photo-resist pattern, the gate line and the data line are formedusing the reverse tapered photo-resist pattern. Because, in the verticalelectric field type LCD, the common electrode is made of transparentconductive material and formed by depositing on the whole surface of theupper substrate, it is not required to reduce the width of the commonelectrode. Further, the pixel electrode is generally transparentconductive material.

In the method for fabricating the TFT array panel according to thepresent invention, the conductive patterns including the pixelelectrode, common electrode, gate line and data line are formed usingthe reverse tapered photo-resist pattern. Therefore, the TFT array panelaccording to the present invention enhances the aperture ratio of thepixel region because the line widths of the pixel electrode and thecommon electrode can be reduced. Further the brightness of the TFT arraypanel according to the present invention is also enhanced.

Additionally, without enhancing the aperture ratio, the pixel number canbe increased by disposing more pixels at the area increased by reducingthe widths of the conductive lines which include the pixel electrode,common electrode, gate line and data line. Using the present invention,it is possible to enhance the aperture ratio and the brightness of theTFT array panel or to increase the pixel number to configure a higherresolution display panel.

It will be apparent to those skilled in the art that variousmodifications and variation can be made in the present invention withoutdeparting from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A method for fabricating a liquid crystal display device, comprising:forming a gate line, a gate electrode connected to the gate line, acommon electrode and a common line connected to the common electrode ona substrate in a first mask process; depositing a gate insulating layeron the substrate to cover the gate line, the gate electrode and thecommon electrode; forming an active layer on the gate insulating layer,the active layer overlapping the gate electrode to form a channel layer,and forming an ohmic contact layer on the active layer in a second maskprocess; forming a data line crossing the gate line to define a pixelregion, a source electrode connected to the data line, and a drainelectrode facing the source electrode in a third mask process;depositing a protective layer over the data line, the source electrodeand the drain electrode; forming a pixel contact hole that exposes thedrain electrode by penetrating the protective layer in a fourth maskprocess; and forming a pixel electrode that generates a horizontalelectric field with the common electrode in the pixel region, whereinthe pixel electrode is connected to the drain electrode through thepixel contact hole in a fifth mask process using a reverse taperedphoto-resist pattern.
 2. The method for fabricating a liquid crystaldisplay device according to the claim 1, wherein the first mask processuses a reverse tapered photo-resist pattern.
 3. The method forfabricating a liquid crystal display device according to the claim 1,wherein the second mask process uses a reverse tapered photo-resistpattern.
 4. The method for fabricating a liquid crystal display deviceaccording to the claim 1, wherein the third mask process uses a reversetapered photo-resist pattern.
 5. The method for fabricating a liquidcrystal display device according to the claim 1, wherein the fourth maskprocess uses a reverse tapered photo-resist pattern.
 6. The method forfabricating a liquid crystal display device according to the claim 1,further comprising forming a gate pad at an end of the gate line in thefirst mask process and a data pad at an end of the data line in thethird mask process.
 7. The method for fabricating a liquid crystaldisplay device according to the claim 1, wherein the reverse taperedphoto-resist pattern has a bottom width of about 4.5 μm.
 8. The methodfor fabricating a liquid crystal display device according to the claim1, wherein at least one of the pixel electrode, common electrode, thegate line, the data line and the common line has a line width of about1.5˜4.0 μm.
 9. The method for fabricating a liquid crystal displaydevice according to the claim 1, wherein at least one of the gateelectrode, the source electrode and the drain electrode has a line widthof about 1.5˜4.0 μm.
 10. The method for fabricating a liquid crystaldisplay device according to the claim 1, wherein the reverse taperedphoto-resist pattern is formed by steps of: depositing photo-resist onthe substrate; baking the photo-resist with controlling temperature forthe photo-resist pattern to have reverse tapered shape and; exposing thephoto-resist with adjusting defocus amount and exposure amount forpatterning the photo-resist to have reverse tapered shape.
 11. A methodfor fabricating a liquid crystal display device, comprising: forming agate line, a gate electrode connected to the gate line, a commonelectrode and a common line connected the common electrode on asubstrate in a first mask process; depositing a gate insulating layer onthe substrate to cover the gate line, the gate electrode and the commonelectrode; forming an active layer on the gate insulating layer, theactive layer overlapping the gate electrode to form a channel layer, andforming an ohmic contact layer on the active layer, a data line crossingwith the gate line to define a pixel region and a source-drain patternconnected to the data line in a second mask process; depositing aprotective layer over the data line, the source electrode and the drainelectrode; patterning the source-drain pattern to form a sourceelectrode and a drain electrode, completing the channel layer byremoving a portion of the ohmic contact layer between the sourceelectrode and the drain electrode, and forming a pixel contact holeexposing the drain electrode by penetrating the protective layer in athird mask process; and forming a pixel electrode that generates ahorizontal electric field with the common electrode in the pixel region,wherein the pixel connects electrode to the drain electrode through thepixel contact hole in a fourth mask process using a reverse taperedphoto-resist pattern.
 12. The method for fabricating a liquid crystaldisplay device according to the claim 11, wherein the reverse taperedphoto-resist pattern has a bottom width of about 4.5 μm.
 13. The methodfor fabricating a liquid crystal display device according to the claim11, wherein at least one of the pixel electrode, common electrode, thegate line, the data line and the common line has a line width of about1.5˜4.0 μm.
 14. The method for fabricating a liquid crystal displaydevice according to the claim 11, wherein a surface of the active layeris exposed by removing the portion of ohmic contact layer between thesource electrode and the drain electrode and treated by oxygen plasma inthe third mask process.
 15. The method for fabricating a liquid crystaldisplay device according to the claim 11, wherein the reverse taperedphoto-resist pattern is formed by steps of: depositing photo-resist onthe substrate; baking the photo-resist with controlling temperature forthe photo-resist pattern to have reverse tapered shape and; exposing thephoto-resist with adjusting defocus amount and exposure amount forpatterning the photo-resist to have reverse tapered shape.
 16. A methodfor fabricating a liquid crystal display device, comprising: forming agate line and a gate electrode connected to gate line on a lowersubstrate using a reverse tapered photo-resist pattern; forming a dataline crossing the gate line to define a pixel region, a source electrodeconnected to the data line, and a drain electrode facing the sourceelectrode on the lower substrate using a reverse tapered photo-resistpattern; forming a pixel electrode in the pixel region connecting to thedrain electrode on the lower substrate; and forming a common electrodeon a upper substrate facing the lower substrate to form a verticalelectric field with the pixel electrode.
 17. The method for fabricatinga liquid crystal display device according to the claim 16, wherein thereverse tapered photo-resist pattern has a bottom width of about 4.5 μm.18. The method for fabricating a liquid crystal display device accordingto the claim 16, wherein at least one of the gate line and the data linehas a line width of about 1.5˜4.0 μm.
 19. The method for fabricating aliquid crystal display device according to the claim 16, wherein thereverse tapered photo-resist pattern is formed by steps of: depositingphoto-resist on the substrate; baking the photo-resist with controllingtemperature for the photo-resist pattern to have reverse tapered shapeand; exposing the photo-resist with adjusting defocus amount andexposure amount for patterning the photo-resist to have reverse taperedshape.